Conventionally there is a known technique that allows data exceeding the capacity of a main memory such as dynamic random access memory (DRAM) to be stored into a space (which may be referred to as a swap file) reserved in a storage (for example, HDD or SSD) other than the main memory to run an application while executing swapping (data moving processing) including moving a page from the main memory to swap space (page-out) and moving a page from swap space to the main memory (page-in).
When such swapping takes place, the speed performance of the application is significantly reduced or becomes unstable (becomes difficult to predict). Systems therefore are usually designed to include a large-capacity memory to ensure a sufficient size of main memory in order to minimize swapping.
Unfortunately, in the conventional technique, electric power that is necessary for at least holding the content of the stored data is kept supplied to all the regions in the large-scale main memory, which makes it difficult to save power consumed by the main memory. On the other hand, reducing the size of the main memory in favor of power saving, in turn, significantly reduces the speed performance of the application running on the processor. Accordingly, it has been difficult to save power while ensuring the speed performance of the application running on the processor.